The present invention deals with the necessity for separation of coolants used in the edge grinding of ophthalmic lenses made of glass and the coolants used in the edge grinding of ophthalmic lenses made of plastic.
Presently, the machines used to grind, shape and bevel ophthalmic lenses are equipped with diamond wheels. The use of high speed diamond wheels makes it necessary to use coolants which promote grinding speed as well as grinding quality. It has been found, however, that the best coolant for edging glass is not the best coolant for the edging of plastic lenses and vice versa. Moreover, after grinding or edging glass lenses, the coolant becomes contaminated with glass particles which have been ground away from the lens. If then a plastic lens is set for edging in the same machine without changing the coolant, the glass particles, in a state of suspension in the coolant, will impinge on the plastic lens which will then be scratched, these scratches will then appear as hairlines on the plastic lens. This is why many machine manufacturers recommend two separate machines; one for plastic and one for glass lenses.
The type of machine under consideration is disclosed in detail in U.S. Pat. No. 3,745,720.